Not Applicable
Not Applicable
1. Field of the Invention
This invention is in the field of equipment and procedures used to apply cooling to living tissue for the purpose of causing, at a minimum, retardation of the proliferation and healing of the tissue. In certain cases, it will be desirable to freeze the tissue so as to render it non-viable.
2. Background Information
In several systems of the body of a patient, it can be desirable to apply extreme cooling to the living tissues, thereby retarding proliferation and healing of the tissues, or rendering the tissues non-viable. The non-viable tissue may then slough off for eventual removal or disintegration, or the tissue may remain in place. Some systems in which this process may be performed are the cardiovascular system and the female reproductive system. In applying this extreme cooling, it is known to introduce a refrigerant through a flexible transvascular catheter, or through a rigid probe. In known systems, the cooling is then applied to the target tissue with a heat transfer element formed as a part of the catheter or probe.
In known systems, the heat transfer element is generally limited to applying the cooling at a relatively small location, since the heat transfer element must be small enough to permit its easy introduction into the treatment area. This means that it may be necessary to apply cooling for a relatively long period of time, in order to freeze surrounding fluid in the system, such as blood in an artery or vein, before the cooling power is applied to the actual target tissue. Alternatively, it may be necessary to shift the heat transfer element to several locations, with repetitive cooling steps, in order to cover the entire target area. It would be helpful, then, to have an apparatus and procedure which will place a heat transfer element which is large enough to contact all the target tissue directly, at one time, thereby allowing the freezing of all the target tissue in one step.
Also in known systems, the application of cooling power to the target tissue may be reduced by the flow of warm fluid past the target area, such as blood flowing past an area of target tissue in an artery or vein. It would be helpful, then, to have an apparatus and procedure which will block the flow of any surrounding fluid, to accelerate the freezing process in the target tissue.
One procedure which could benefit from the freezing of tissue is the practice of angioplasty, in which a balloon is inflated to open up a region of stenosis in an artery supplying blood to the heart. It is commonly known that, after the performance of the angioplasty procedure, the area of stenosis will often experience restenosis. It would be helpful, then, to have an apparatus and procedure to freeze the arterial wall tissue in the area of the stenosis, thereby rendering it non-viable, to prevent restenosis.
By way of example, the subject invention provides an apparatus and a method for inserting a balloon catheter into a selected location in a vascular system of a patient. When the balloon is positioned in the selected location, the balloon is inflated to contact the walls of the vascular system, such as the walls of a blood vessel. This inflation may, for example, be achieved by expanding a compressed refrigerant into the balloon, or it may be achieved by introducing a separate pressurized fluid through the catheter into the balloon. The expanded refrigerant cools either the balloon or a separate heat transfer element, to freeze the surrounding tissue. Where used, the separate heat transfer element can be a metallic coil wound around the catheter next to the balloon, or a metallic cylinder on the outside surface of the catheter next to the balloon. If the inflated balloon is used as the heat transfer device, the cooling is applied directly to the walls of the vascular system. If a separate heat transfer element is used, freezing of surrounding fluid in the vascular system, such as blood, may be necessary, forming an ice ball which will ultimately freeze the walls of the vascular system. The apparatus and method of the invention may be used, for example, to open restricted areas of a blood vessel.
The novel features of this invention, as well as the invention itself, will be best understood from the attached drawings, taken along with the following description, in which similar reference characters refer to similar parts, and in which: